Atlassian Coding Interview Questions
25 Atlassian coding interview problems with full optimal solutions — 4 easy, 18 medium, 3 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Atlassian interviewer values, and a FAQ section.
Showing 25 problems of 25
- #1easyfoundational
1. Two Sum
Two Sum is Atlassian's canonical phone-screen warm-up: given an integer array and a target, return the indices of the two numbers that add to the target. Atlassian uses it to confirm you can code and articulate the brute-to-optimal tradeoff before a harder graph or design follow-up.
3 free resourcesSolve → - #3mediumfrequently asked
3. Longest Substring Without Repeating Characters
Longest Substring Without Repeating Characters is the canonical Atlassian sliding-window problem. Given a string s, return the length of the longest substring without repeating characters. Atlassian uses it to gate whether you understand the two-pointer / sliding-window pattern.
4 free resourcesSolve → - #20easyfoundational
20. Valid Parentheses
Valid Parentheses is Atlassian's stack-introduction warm-up. Given a string containing only the characters '()', '[]', and '{}', determine if the input is properly matched. Atlassian uses it to check you know when to reach for a stack before pivoting to a harder parsing question.
3 free resourcesSolve → - #49mediumfrequently asked
49. Group Anagrams
Group Anagrams is an Atlassian favorite because it mirrors the bucket-by-canonical-key idea behind Confluence search and Jira tag dedupe. You're given an array of strings; return the strings grouped so each group contains anagrams of one another.
3 free resourcesSolve → - #56mediumcompany favorite
56. Merge Intervals
Merge Intervals is an Atlassian-favorite scheduling problem. Given an array of intervals [start, end], merge all overlapping ones and return the result. It maps directly to calendar coalescing in Atlassian's Confluence calendars and Jira time-tracking UIs.
4 free resourcesSolve → - #79mediumfrequently asked
79. Word Search
Word Search is an Atlassian DFS-backtracking problem. Given a grid of characters and a target word, return true if the word can be constructed from adjacent (horizontal/vertical) letters with no cell reused. Atlassian uses it to check whether you can write backtracking that cleans up after itself.
4 free resourcesSolve → - #98mediumfrequently asked
98. Validate Binary Search Tree
Validate Binary Search Tree is an Atlassian classic for testing whether you understand the recursive invariant of a BST. Return true if a given binary tree is a valid BST. The naive 'check children' answer is wrong, and Atlassian uses this exact gap to grade rigorous thinkers.
4 free resourcesSolve → - #102mediumfrequently asked
102. Binary Tree Level Order Traversal
Binary Tree Level Order Traversal is the canonical Atlassian BFS-on-a-tree problem. Return the nodes' values level by level (left to right, one array per level). Atlassian uses it to confirm you can write BFS without smearing levels together.
4 free resourcesSolve → - #121easyfoundational
121. Best Time to Buy and Sell Stock
Best Time to Buy and Sell Stock is an Atlassian warm-up that tests whether you notice the linear single-pass pattern. Given an array of daily prices, return the maximum profit from one buy then one sell. The trap is brute-forcing every (buy, sell) pair when one pass suffices.
4 free resourcesSolve → - #127hardfrequently asked
127. Word Ladder
Word Ladder is the canonical Atlassian BFS-on-implicit-graph problem. Given beginWord, endWord, and a dictionary, return the length of the shortest transformation sequence such that each step changes one letter and every intermediate word is in the dictionary. Atlassian uses it to test whether you can identify when BFS is the right tool.
4 free resourcesSolve → - #139mediumfrequently asked
139. Word Break
Word Break is an Atlassian-favorite dynamic programming problem. Given a string s and a dictionary, determine whether s can be segmented into a space-separated sequence of dictionary words. Atlassian uses it to test memoization intuition before harder string-DP follow-ups.
4 free resourcesSolve → - #146mediumcompany favorite
146. LRU Cache
LRU Cache is Atlassian's classic OOP-and-data-structure design problem. Design a fixed-capacity cache that evicts the least-recently-used key on overflow with O(1) get and put. Atlassian asks it to test whether you can combine a doubly-linked list with a hash map without dropping pointer invariants under pressure.
4 free resourcesSolve → - #200mediumfrequently asked
200. Number of Islands
Number of Islands is Atlassian's canonical grid-graph problem. Given an m x n grid of '1' (land) and '0' (water), return the number of distinct land islands. Atlassian asks it because grid traversal under-pressure is a clean signal for whether you can navigate Jira's board layouts or Confluence's page trees.
4 free resourcesSolve → - #206easyfoundational
206. Reverse Linked List
Reverse Linked List is Atlassian's pointer-manipulation warm-up. Given the head of a singly linked list, reverse the list and return the new head. The grading focus is correct three-pointer rewiring without dropping nodes or creating cycles.
4 free resourcesSolve → - #207mediumcompany favorite
207. Course Schedule
Course Schedule is an Atlassian-favorite graph problem because it mirrors Jira's dependency model. Given numCourses and a list of prerequisite pairs, determine whether you can finish all courses — equivalent to detecting a cycle in a directed graph.
4 free resourcesSolve → - #208mediumcompany favorite
208. Implement Trie (Prefix Tree)
Implement Trie is an Atlassian-favorite OOP-design problem because tries power Confluence's @-mention autocomplete and Jira's smart label search. You design a prefix tree supporting insert, search (full word), and startsWith (prefix). The grading focus is clean class structure and pointer ownership.
4 free resourcesSolve → - #215mediumfrequently asked
215. Kth Largest Element in an Array
Kth Largest Element in an Array is an Atlassian heap-vs-quickselect classic. Given an integer array and an integer k, return the kth largest element. The grading is whether you can compare the heap, sort, and quickselect tradeoffs without hand-waving.
4 free resourcesSolve → - #253mediumcompany favorite
253. Meeting Rooms II
Meeting Rooms II is an Atlassian-favorite resource-allocation problem. Given an array of meeting time intervals, return the minimum number of rooms required so every meeting can run without conflicts. It maps directly to Atlassian's Confluence team-calendar scheduler.
4 free resourcesSolve → - #295hardfrequently asked
295. Find Median from Data Stream
Find Median from Data Stream is Atlassian's two-heap design problem. Numbers arrive one at a time; return the median after every insert. Atlassian asks it because the same pattern appears in their Confluence analytics dashboards that surface live percentiles.
4 free resourcesSolve → - #297hardfrequently asked
297. Serialize and Deserialize Binary Tree
Serialize and Deserialize Binary Tree is an Atlassian-favorite design problem. Implement two methods that convert a binary tree to a string and back, with no shared state between them. Atlassian asks it because it tests cleanly whether you can pick an unambiguous traversal and reverse it.
4 free resourcesSolve → - #322mediumfrequently asked
322. Coin Change
Coin Change is an Atlassian-favorite dynamic programming problem. Given coin denominations and a target amount, return the fewest coins needed to make the amount, or -1 if impossible. Atlassian asks it because the bottom-up DP solution is a clean signal for whether you can write a tabular DP from a recurrence.
4 free resourcesSolve → - #347mediumfrequently asked
347. Top K Frequent Elements
Top K Frequent Elements is Atlassian's heap-and-counting interview classic. Given an integer array and an integer k, return the k most frequent elements. Atlassian asks it because top-k ranking is the algorithmic backbone behind Confluence's 'most active pages' and Jira's 'top reporters' surfaces.
4 free resourcesSolve → - #348mediumcompany favorite
348. Design Tic-Tac-Toe
Design Tic-Tac-Toe is Atlassian's OOP-design problem. Implement a game where two players take turns marking cells; the move method returns the current player's win state. The grading focus is O(1) per move using per-row, per-column, and diagonal counters — not a full board scan.
4 free resourcesSolve → - #560mediumfrequently asked
560. Subarray Sum Equals K
Subarray Sum Equals K is an Atlassian-favorite prefix-sum + hash-map problem. Given an integer array and an integer k, return the total number of subarrays whose sum equals k. The unsigned reveal is that prefix sums + hash map is the optimal — sliding window fails when negatives appear.
4 free resourcesSolve → - #973mediumfrequently asked
973. K Closest Points to Origin
K Closest Points to Origin is Atlassian's canonical heap-introduction problem. Given an array of points and an integer k, return the k points closest to (0,0) by Euclidean distance. Atlassian uses it as the first step toward more complex top-k ranking systems in their search UI.
4 free resourcesSolve →
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